Half of all ovarian cancer patients die within five years. This is largely because their tumors recur after chemotherapy and metastasize within the intraperitoneal cavity, eventually blocking function of organs such as the bowel. Additionally, no FDA-approved drugs block the steps of intraperitoneal metastasis. Thus, new strategies are needed to prevent ovarian cancer metastasis. This proposal focuses on the receptor tyrosine kinase Discoidin Domain Receptor 2 (DDR2) as a candidate target to prevent ovarian cancer metastasis for the following reasons. First, DDR2 is overexpressed in 74% of advanced-stage, high-grade serous human ovarian tumors and 100% of metastases. Second, patients whose tumors had higher levels of DDR2 had shorter survival than those with lower levels of DDR2. Third, preliminary data shows that, after tumor cell injection, tumors formed in syngeneic DDR2 knockout mice were smaller and contained less collagen (the ligand for DDR2) than those in DDR2 wild-type mice. Fourth, promising small molecule DDR2 inhibitors have been developed that, unlike all other receptor tyrosine kinase inhibitors, bind and allosterically inhibit the extracellular domain of DDR2. This proposal will test the central hypothesis that DDR2 in stromal cells promotes steps of metastasis by acting through its ligand collagen to alter the microenvironment. Aim 1 will build on strong preliminary data showing that DDR2 in the stroma promotes metastasis by identifying the particular stromal cells (fibroblasts and mesothelial cells) and steps in which DDR2 contributes to metastasis. This aim will make use of a large bank of human primary omental stromal cells and ovarian tumor cells. Aim 2 will test the hypothesis that DDR2 in the mesothelial cells, fibroblasts, or both is activated by collagen I, leading to increased matrix metalloprotease 2 activity and fibronectin cleavage. Additionally, this aim will test the hypothesis that DDR2 regulates collagen amount and organization in the microenvironment and will identify proteins secreted by DDR2-expressing fibroblasts that promote ovarian tumor cell invasion. Aim 3 will assess the ability of a novel DDR2 inhibitor to enhance response to chemotherapy, and identify tumor microenvironment components that correlate with response. In addition to testing a novel DDR2 inhibitor in mouse syngeneic and patient-derived xenograft models of ovarian cancer, this aim will use a novel, multi-parameter fluorescent imaging tool to define tumor/stromal cell expression patterns and extracellular matrix signatures that correlate with treatment response in mouse and human tumors. Completion of these aims will uncover novel mechanisms by which the tumor microenvironment contributes to intraperitoneal metastasis and reveal new potential targets for therapy.